Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $53.71   12.180%   $60.2519   $60.25   $60.25   $60.30  
  Purchase #2 $238.92   3.439%   $247.1365   $247.14   $247.15   $247.10  
  Purchase #3 $28.65   3.689%   $29.7069   $29.71   $29.70   $29.70  
  Purchase #4 $227.51   6.331%   $241.9137   $241.91   $241.90   $241.90  
  Purchase #5 $131.44   7.794%   $141.6844   $141.68   $141.70   $141.70  
  Purchase #6 $190.71   11.306%   $212.2717   $212.27   $212.25   $212.30  
  Purchase #7 $74.49   7.658%   $80.1944   $80.19   $80.20   $80.20  
  7 purchase totals = $945.43       $1,013.1595   $1,013.15   $1,013.15   $1,013.20